The error message 'value sent to Redis cannot be null' is typically caused by attempting to set a key in Redis with a null value. Redis does not allow null values to be stored as values for keys. If the application attempts to set a key with a null value, Redis will return this error message.
Another possible cause of this error could be an issue with the serialization or deserialization of data. Redis stores data in memory as byte arrays, so data needs to be serialized and deserialized when it is sent to and received from Redis. If there are issues with the serialization or deserialization process, this can result in null values being sent to Redis.
To resolve this error, you should ensure that your application does not attempt to set keys with null values. You can add checks to your code to validate that the values being set are not null before sending them to Redis. Alternatively, you can consider setting default values for keys if the values being set are null.
If the issue is related to serialization or deserialization, you should check your application's implementation of these processes. Confirm that the data is being properly serialized and deserialized before being sent to or received from Redis. You may also consider using a serializer specifically designed for Redis, such as the StackExchange.Redis library, which offers built-in serialization and deserialization support.